This invention relates generally to circuit boards for electronic circuits and more particularly to connectors for such circuit boards that may be used in a stacked configuration.
The development of the integrated circuit has greatly reduced the size of electronic circuits and their components. This reduction in size, however, must at some point become compatable with larger devices and systems which either cannot be reduced or won't be reduced beyond a certain point. For example, switches, dials and meters are limited to the point where human hands can operate and human eyes can see them.
The individual circuit that is commonly utilized today is of such small size that it is impractical to be repaired within the unit in which it functions. As a result, the circuits are placed on flat planar structures easily inserted or removed from the device. As a practical matter, connections for these circuits are brought to the edge of structure. They then connect to some type of connecting means which will carry the electrical signal or potential either to or away from the circuit. Packaging of the circuits controls the means and methods used to connect the circuits and structures on which they are mounted.
Present packaging trends are toward the use of large scale integrated circuits and dense interconnection of these circuits and other components using hybrid techniques. The resulting hybrid packages are characterized by high density "in-out" leads, often coming out all four sides of the circuit, and by high power densities. Frequently, it is desirable and necessary to inter-connect many of these hybrids in as small a volume as possible to save space and weight in aerospace equipment. In addition, requirements for short signal delays and for new technologies may also dictate that these components be packaged as close together as possible. These requirements for dense packaging put extreme pressure on the designer to reduce the volume required for interconnections between the circuit packages which in turn increases the system power density.
There has been a need seen for some method and means to provide a motherboard on more than one side of a stack of circuit structures. If such a solution included a motherboard on up to four sides of the circuit structure the packaging need would be met.
Several methods have been attempted in the past but have not proven entirely adequate, although providing some relief for the problem. Such methods include, stacked memory modules with riser ribbons, stacked printed circuit cards with compression connectors between layers, stacks of packages with leads on two or more sides interconnected with printed circuit cards, and permanently interconnected stacks of circuit cards. Other programs have been suggested with packages stacked with very precisely machined carriers and motherboard hardwear.
These systems have all failed to gain wide acceptance since they do not provide the characteristics necessary to make them small, reliable, strong, light weight and inexpensive. Further, such systems must provide easy access to all inter package signals for trouble shooting; must be easily disassemblable for replacement or repair of parts; provide for adequate thermal protection and able to accommodate discrete components such as inductors, transformers, and physically large capacitors where necessary.